Remarkable progress has been made over the past decade in the molecular imaging of atherosclerotic lesion. The majority of studies have focused on the peptide based probes, which is monovalent and rapidly cleared from systemic circulation, leading to low targeting efficiency and contrast ratio. Thus, more and more efforts are toward using nanoparticle based molecular probe for targeted plaque imaging due to the tunable pharmacokinetics and multivalency. Of various nanoplatforms, core-shell polymeric nanoparticles are of particular interest owing to the flexible design of structures with accurate control of functional groups for multi- applications. Among an array of biomarkers upregulated on atherosclerotic lesion, chemokine receptors are promising targets owing to their critical roles in the initialization and progression of disease. Recently, we have developed chemokine receptors targeted Comb nanoparticles conjugated with novel peptides and labeled with 64Cu for atherosclerosis PET imaging. These targeted nanoagents demonstrated the sensitivity and targeting specificity in experimental mouse ApoE-/- model. In the proposed project, we will optimize the construction of viral macrophage protein-II (vMIP-II) conjugated Comb nanoparticles targeting a group of chemokine receptors and D-ala-peptide T-amide (DAPTA) conjugated Comb nanoparticles specifically targeting CCR5. Our preliminary PET imaging showed specific accumulation of 64Cu-vMIP-Comb and 64Cu-DAPTA-Comb at the aortic arch in ApoE-/- mice. However, the targeting efficiency and target-to-background ratio need further improvement. Thus, we will increase the number of vMIP-II peptide conjugated on each Comb nanoparticle and optimize the pegylation for enhanced targeting efficiency and reduce the blood circulation for minimized non-specific binding. The preferred vMIP-Comb will be used to determine the sensitivity and specificity in early stage of atherosclerosis. For DAPTA-Comb, we will follow the same strategy to optimize the nanostructure for in vitro screening in CCR5+ cell line. The candidate DAPTA-Com will be evaluated in ApoE-/- mice with significant lesion (Specific Aim 1). Then we will use the candidate vMIP-Comb and DAPTA-Comb to determine whether they can detect variation in atherosclerosis burden or progression. We will further analyze the specific cell type associated with radiolabeled nanoparticles in atherosclerotic lesion and correlate the PET signals obtained with the two nanoagents to the pathological examination including plaque area and macrophage area (Specific Aim 2). We anticipate that the targeted nanoparticles will provide sensitive and specific detection of chemokine receptors at plaque and serve as useful tools to detect the burden and progression of atherosclerotic plaque.